What Does P0731 Mean?
The TCM has detected that the actual gear ratio in 1st gear does not match the expected ratio. The calculated ratio from the input and output shaft speed sensors deviates beyond the allowable threshold when 1st gear is commanded. The driver may notice slipping when accelerating from a stop, engine flare (RPM rise without corresponding speed increase), delayed or harsh 1st gear engagement, or the vehicle feeling like it starts in a higher gear.
Common Causes
35%
Worn 1st gear clutch pack or low-reverse band with reduced friction capacity causing slippage
25%
Low transmission fluid or contaminated fluid reducing hydraulic clutch apply pressure
20%
Failed or weak pressure control solenoid delivering insufficient apply pressure to the 1st gear circuit
10%
Faulty input or output shaft speed sensor causing incorrect ratio calculation
10%
Valve body wear or stuck 1st gear apply valve causing reduced hydraulic flow
Diagnostic Steps
1
Check transmission fluid level and condition. Low or burnt fluid is a primary cause of 1st gear slippage. Perform a drain and fill if the fluid is dark or contaminated.
2
During a road test, monitor ISS and OSS in live data while accelerating from a stop in 1st gear. Calculate the ratio and compare to the factory specification (typically 2.5–4.0:1 depending on transmission).
3
Perform a stall test in Drive (with wheels chocked and brake applied firmly) — note the stall RPM. Higher-than-specified stall RPM indicates 1st gear clutch slippage.
4
Test the pressure control solenoid and the solenoid(s) involved in 1st gear apply — measure resistance, current draw, and duty cycle response using the scan tool.
5
Connect a pressure gauge to the line pressure test port and the 1st gear clutch apply circuit (if accessible). Compare to specifications in each gear range.
Estimated Repair Cost
$150 - $3,500
Parts + labor, varies by vehicle and location
The TCM has detected that the actual gear ratio in 1st gear does not match the expected ratio. The calculated ratio from the input and output shaft speed sensors deviates beyond the allowable threshold when 1st gear is commanded. The driver may notice slipping when accelerating from a stop, engine f...
The most common cause of P0731 (Gear I Incorrect ratio) is: Worn 1st gear clutch pack or low-reverse band with reduced friction capacity causing slippage
Typical repair costs for P0731 range from $150 to $3,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Slipping in 1st gear means the vehicle may not accelerate as expected from a stop, which is dangerous when pulling into traffic or crossing intersections. Continued driving with a slipping clutch pack generates heat and accelerates wear. Have the transmission diagnosed promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0731 to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission / Gear Ratio Control
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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